1. Field of the Invention
The present invention relates generally to a system and method for removing and/or separating an interleaf sheet from a plate sheet and/or transporting a plate sheet, used in connection with, for example, Computer-to-Plate (CTP) imaging systems.
2. Background Description
Automating the printing process in CTP imaging systems involves the alternating process of extracting plate sheet material, and then interleaf sheet material, from a material stack. Images are exposed on the plate sheet material, and the interleaf sheet material is used to protect the imaging surface of plate sheets from each other.
Interleaf sheets, though varying from manufacturer to manufacturer in material characteristics such as smoothness, porosity, and color, are generally paper-like with a thickness of about 0.003 inches. Plate sheet material typically varies in thickness from 0.005 inches to 0.012 inches.
Extracting the interleaf sheets manually is labor intensive, but normally does not present other issues or challenges. However, automating the process for extracting interleaf sheets can be challenging. For example, interleaf sheets can adhere onto the imaging surface of the plate sheet because of, for example, friction and/or static. Known CTP systems that automate the removal of interleaf sheets, such as disclosed in U.S. Pat. No. 5,655,452, which is in incorporated herein by reference, use at least a combination of a suction cup and air blast. However, due to the porous nature of the interleaf sheet, reliability issues are generally present when suction cups are used to remove interleaf sheets.
Other known techniques for removing interleaf sheets involve the sole or predominant use of pneumatic techniques, or grippers. For example, gripping can involve the use of two rubber pads that contact an interleaf sheet. The rubber pads are separated before making contact with the interleaf sheet. Subsequent to making contact, the pads are moved closer together, thereby grabbing the interleaf sheet. The pads then lift the interleaf sheet off the stack, and move it to a bin or transport device. The cycle is repeated for each interleaf sheet in the stack. However, the “grabbing” technique has operational and reliability shortcomings.
In addition, the process of removing a plate sheet from an interleaf sheet is difficult to automate. The need is to pick up and remove the plate sheet, without disturbing the position or condition of the interleaf sheet underneath the plate. The interleaf sheet may have vacuum and static electricity forces that cause the interleaf sheet to adhere to the underside of the plate sheet. Conventional systems generally pick up the plate sheet at or near its geometric center. Once the plate sheet is removed from the stack using, for example, suction cups, various sequences of flexing, shaking, air blasting are employed to remove an interleaf sheet that is adhering to the underside of the plate. In the worst case there are multiple plates and interleaf sheets stuck to the top plate. Such conventional systems/mechanisms tend to be relatively large, complicated, and expensive.